Another plot could involve the reader being a magical being, like a fairy or a witch, who is on a mission to protect Ciel from a dark magic that is threatening him. This would create a lot of opportunities for magical elements and a relationship that develops as the reader uses their powers to keep Ciel safe. They might have to go on quests together to find magical artifacts to counter the dark magic. It's a plot full of adventure and mystery.
One great hurt/comfort fanfiction could be 'Ciel's Solace'. In this fic, Ciel experiences a major setback during a case, and Sebastian tries to comfort him in his own unique way. It delves deep into Ciel's vulnerable side, showing how he struggles with his past traumas while Sebastian's presence becomes a source of both annoyance and comfort. The author does a wonderful job of portraying the complex relationship between them in this context.
A fanfiction could explore what would happen if Ciel was sent to Hogwarts. He could be sorted into Slytherin due to his cunning nature. He might find the magic there strange yet useful in his quest for revenge. Harry could befriend him and try to show him a different path than revenge, while Ciel could teach Harry some of his skills in investigation and strategy.
Sure. You can try searching on fanfiction platforms like Archive of Our Own. Look for stories tagged as 'ciel phantomhive x reader' and filter out the ones with mature or lemon tags. There are often many sweet and platonic stories in this category that focus on the relationship between Ciel Phantomhive and the reader in a more innocent way, such as adventure - based stories or ones centered around solving mysteries together.
One common theme is mystery. Given Ciel's own mysterious nature in the 'Black Butler' series, many fanfics incorporate mystery elements into the relationship between Ciel and the reader. For example, the reader might be involved in solving a mystery alongside Ciel.
The exploration of his daily life with asthma is fascinating. How he has to manage his inhalers (if they exist in the fanfic's version), how he copes with physical exertion, and how he hides his condition from his enemies or uses it to his advantage in some cases. All these aspects make Ciel Phantomhive asthma fanfics really interesting.
Some fanfictions might portray Ciel as more vulnerable than he appears in the original. Maybe showing his inner turmoil more openly. Sebastian could be seen as having more human emotions, like a sense of guilt for some of his actions towards Ciel. And then there are the side characters. For instance, Mey - Rin could be given a more complex backstory, perhaps she has a hidden agenda that ties in with Ciel's plans.
One common theme is mystery. Ciel's own past and the secrets of the Phantomhive family often play a big part. Another theme could be revenge, as Ciel is on a quest for vengeance in the original story. And there's also the theme of loyalty, like the loyalty of Sebastian to Ciel which might be further explored or twisted in fanfiction.
One great 'ciel phantomhive x reader fanfiction' is 'A Meeting in the Dark'. It has a really interesting plot where the reader character stumbles upon Ciel's secrets in a very unexpected way. The way the author builds the tension between the two characters is quite engaging.
One plot idea could be the reader being a new servant in the Phantomhive manor. Ciel is initially suspicious but as time passes, he starts to trust and rely on the reader in a unique way. Maybe the reader has a special skill that helps Ciel in his investigations or in dealing with the other nobles.
Maybe in the fanfiction, Ciel's pregnancy is a symbol of a new beginning for the Phantomhive family. It could be a way to redeem the family's past sins. His pregnancy journey could involve him learning more about his family's history and finding a way to make peace with it. As he grows closer to giving birth, he also grows as a person and as a leader.